U.S. patent application number 15/408380 was filed with the patent office on 2018-07-19 for multi-phase, variable frequecy electrospinner system.
The applicant listed for this patent is Ian McClure. Invention is credited to Ryan Bailey, Scott Baskerville, Ian McClure.
Application Number | 20180202075 15/408380 |
Document ID | / |
Family ID | 62838583 |
Filed Date | 2018-07-19 |
United States Patent
Application |
20180202075 |
Kind Code |
A1 |
McClure; Ian ; et
al. |
July 19, 2018 |
MULTI-PHASE, VARIABLE FREQUECY ELECTROSPINNER SYSTEM
Abstract
An apparatus for producing a fibrous material. The apparatus
uses a first material source within which is disposed a first
material and a second material source enclosing a second material.
The first and second materials to be electrospun. A first and
second tip attached to an end of the first and second material
sources, with a collector spaced apart from the first and second
material sources. A first and second electric field generator each
produces a first and second signal each in the form of a sine wave
and having a first and second frequency. The fibers are formed from
the first and second materials as extracted from the respective
first and second tips responsive to a first and second electric
field generated between the respective first and second tips and
the collector.
Inventors: |
McClure; Ian; (Melbourne,
FL) ; Baskerville; Scott; (Melbourne, FL) ;
Bailey; Ryan; (Melbourne, FL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
McClure; Ian |
Melbourne |
FL |
US |
|
|
Family ID: |
62838583 |
Appl. No.: |
15/408380 |
Filed: |
January 17, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 41/006 20130101;
D01D 5/0061 20130101; D01D 5/0092 20130101; B05B 5/008 20130101;
B05B 5/005 20130101; D04H 1/728 20130101 |
International
Class: |
D01D 5/00 20060101
D01D005/00; D04H 1/728 20060101 D04H001/728 |
Claims
1. An apparatus for producing a fibrous material, comprising: a
material source, a material to be electrospun disposed within the
material source: a tip attached to an end of the material source; a
collector spaced apart from the material source; an electric field
generator producing a sine wave as a function of time and a
frequency of the sine wave variable as a function of time; and the
apparatus for electrospinning fibers formed from the material as
extracted from the tip responsive to an electric field generated by
the electric filed generator between the tip and the collector.
2. The apparatus of claim 1 the collector configured to receive the
fibers from the tip.
3. The apparatus of claim 1 further comprising a rotary mechanism
configured to rotate at least one of the material source and the
collector around a longitudinal axis defined by the material
source.
4. The apparatus of claim 3 wherein the rotary mechanism is
configured to rotate both the collector and the collector at
different angular speeds.
5. The apparatus of claim 3, wherein the rotary mechanism is
configured to rotate the material source and the collector in
opposite angular directions.
6. The apparatus of claim 1 wherein the material source comprises a
rotatable material source configured to rotate about a longitudinal
axis defined by the material source.
7. The apparatus of claim 1 wherein at least one of a magnitude and
a frequency of the electric field is controllable to effect one or
more properties of the fibers.
8. The apparatus of claim 1 a flow rate of the fibers ejected from
the tip controllable responsive to the electric field.
9. The apparatus of claim 1 the material comprising any one of a
metal, a composite, or carbon.
10. An apparatus for producing a fibrous material, comprising: a
first material source for storing a first material to be
electrospun; a second material source for storing a second material
to be electrospun; a first tip attached to an end of the first
material source; a second tip attached to an end of the second
material source; a collector spaced apart from the first and second
material sources; a first electric field generator producing a
first signal as a function of time having a first frequency; a
second electric field generator producing a second signal as a
function of time having a second frequency; the apparatus for
electrospinning fibers formed from the first and second materials
as extracted from the respective first and second tips responsive
to a first and second electric field generated between the
respective first and second tips and the collector.
11. The apparatus of claim 10 wherein the first frequency and the
second frequency are equal.
12. The apparatus of claim 11 wherein the first and second signals
are out of phase.
13. The apparatus of claim 10 wherein the first frequency and the
second frequency are not equal.
14. The apparatus of claim 10 the first material comprising a
different material from the second material.
15. An apparatus for producing a fibrous material, comprising: a
material source holding a material to be electrospun; a tip
attached to an end of the material source; a collector spaced apart
from the material source; an electric field generator for producing
first and second signals; the apparatus for electrospinning fibers
formed from the material as extracted from the tip responsive to an
electric field generated between the tip and the collector by the
first and second signals.
16. The apparatus of claim 15 the first signal having a first
frequency and the second signal having a second frequency.
17. The apparatus of claim 16 the first frequency equal to the
second frequency.
18. The apparatus of claim 17 the first signal out of phase with
the second signal.
19. The apparatus of claim 15 at least one of the first and second
signals comprises a square wave signal.
20. The apparatus of claim 15 the material comprising any one of a
metal, a composite, or carbon.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application claims the benefit of U.S.
provisional patent application filed on Jan. 15, 2016 and assigned
Application No. 62/279,067, which is incorporated herein in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to a modulated
signal electrospinner system and specifically to a modulated signal
electrospinner system using multiphase and multifrequency
signals.
BACKGROUND OF THE INVENTION
[0003] A prior art DC electrospinning system produces fibrous
material out of a dissolved or melted solute. This is accomplished
using a combination of chemical principles and high voltage
electricity. A typical DC electrospinner has a solute (normally a
plastic or a polymer) dissolved in a powerful solvent and placed in
syringe or similar fluid storage vessel. The fluid is electrified
from a high voltage DC power supply ranging from about 3.3 KV to
about 100 KV, thereby creating a highly charged medium. This fluid
is then pumped into a syringe nozzle having a diameter of between
about 16 ga and 40 ga.
[0004] In addition to a syringe based electrospinning system,
electrified fluid can be "presented" in the form of a vat that can
be charged either evenly with a mesh, or through more complicated
techniques such as a rolling drum, bubbles, or other mechanisms
that can provide a charge at a point or set of points in the fluid.
Electrospinning has also been accomplished through mechanical means
of a charged, high speed spinning wheel coated in the
electrospinning fluid.
[0005] Nanofibers, which can be formed using an electrospinning
system are useful in a variety of fields from clothing industry to
military applications. For example, in the bio-substance field,
nanofibers provide a scaffolding for tissue growth effectively
supporting living cells. In the textile field, nanofibers have a
high surface area per unit mass that provides light but highly
wear-resistant garments. Carbon nanofibers are used in reinforced
composites, in heat management, and in reinforcement of elastomers.
Many potential nanofiber applications are under development as the
ability to manufacture and control their chemical and physical
properties improves.
[0006] Electrospinning techniques are used to form particles and
fibers as small as one nanometer in a principal direction. The
related concept of electrospray forms a droplet of a polymer melt
at an end of a needle. An electric field charges the droplet and
parts of the droplet are expelled because of the repulsive electric
force due to the electric charges. A solvent present in the parts
of the droplet evaporates and small particles are formed.
[0007] The electrospinning technique is similar to the electrospray
technique. However, during expulsion fibers are formed from the
liquid as the parts are expelled from the needle.
[0008] The fibers are drawn toward a grounded metal object, called
the collector, which is positioned a predetermined distance from
the electrospinning fluid source. This object may comprise, for
example, a plate or a rotating drum; but the collector object must
be grounded or have a negative charge, either will work in a DC
system.
[0009] As the charged fluid exits the source and flows toward the
grounded collector (or the charged fluid in the vat), it begins to
form a Taylor Cone at the tip of the nozzle (or for the charged
fluid in the vat, at the closest point of the fluid to the
collector). A Taylor Cone is a cone-shaped fluid mass formed at the
very tip of the nozzle and extending from and external to the
nozzle. In a vat system, multiple Taylor cones form on the closest
surface, whether that be the electrified fluid surface, a roller,
bubble, or other charge focusing mechanisms.
[0010] A basic electrospinning apparatus 10 is shown in FIG. 1 for
the production of nanofibers and other material fibers. The
apparatus 10 creates an electric field 12 that guides a polymer
melt or solution 14 (i.e., a fluid mass) extruded from a tip 16 of
a needle 18 to a grounded object or electrode 20. A nozzle 22
stores the polymer solution 14. Conventionally, one end of a
voltage source (not shown) is electrically connected directly to
the needle 18, and the other end of the voltage source is connected
to the electrode 20. The electric field 12 created between the tip
16 and the electrode 20 causes the solution 14 to overcome cohesive
forces that hold the polymer solution together, causing a jet of
the solution 14 to be drawn from the tip 16 toward the electrode 20
by the electric field 12 (i.e., a process referred to as electric
field extraction). The polymer dries during flight from the needle
18 to the electrode 20 to form fibers. The fibers are typically
collected downstream on the electrode 20.
[0011] A polymer solution is one example of the different materials
that can be used to form the fibers.
[0012] FIGS. 2A, 2B, and 2C illustrate successive steps in the
formation of the Taylor Cone at the tip 16. FIG. 2A illustrates the
tip 16 with no fluid in the nozzle 18. FIG. 2B illustrates the tip
16 with a fluid mass 14, but without a voltage differential between
the fluid and a spaced-apart grounded object (not shown in FIG.
2B). FIG. 2C illustrates the Taylor Cone 21 as it begins to from as
the charged fluid 14 exits the tip 16 and flows toward the
collector 20.
[0013] Within the tip 10, the charged fluid begins to form fibers
due to the significant charge differential between the electrified
fluid and grounded collector. The charged fluid within the tip
attempts to lower its energy state by shorting to the collector,
forming charged fibers and ejecting the charged fibers from the
Taylor cone tip. In just a few minutes, a copious amount of the
fluid is piled on the collector as loose and random fibers if the
collector is a plate or flat surface. If the collector is a
rotating drum the fibers are disposed on the drum as loose but
aligned fibers.
[0014] The inability to control fiber formation and fiber
structure, and the lack of interconnection between the fibers makes
electrospun fibers of questionable value for scaffolding purposes
or for making nanostructures of any useable mechanical strength or
having desirable physical properties. Given these disadvantages,
there is no technique for creating a controlled nanostructure,
beyond very small scale production.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The skilled artisan will understand that the drawings,
described below, are for illustration purposes only. The drawings
are not intended to limit the scope of the present invention in any
way.
[0016] FIG. 1 illustrates an eletrospinner system.
[0017] FIGS. 2A, 2B, and 2C illustrate successive steps in the
formation of a Taylor cone during the electrospinning process.
[0018] FIG. 3 illustrates a sine wave for use with the
electrospinner system of FIG. 1.
[0019] FIGS. 4 and 5 illustrate a block diagram electrospinner
systems.
[0020] FIG. 6 is a scanning electron micrograph of a fiber material
constructed according to the teachings of the present
invention.
[0021] FIGS. 7-12 illustrate various signal waveforms suitable for
use with the electrospinning system of the present invention.
[0022] FIG. 13 illustrates a block diagram of electrospinning
system for use with three fibers.
[0023] FIG. 14 illustrates vacuum tube types for use with the
present invention.
[0024] FIGS. 15-17 illustrate vacuum tube embodiments for use with
the present invention.
[0025] FIG. 18 illustrates waveforms of the present invention.
[0026] FIGS. 19 and 20 illustrate scanning electron micrographs of
fiber materials constructed according to the teachings of the
present invention.
[0027] FIG. 21 illustrates a carbon fiber electrospinning
system.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Before describing in detail the particular methods and
apparatuses related to an electrospinning process, it should be
observed that the embodiments of the present invention reside
primarily in a novel and non-obvious combination of elements and
method steps. So as not to obscure the disclosure with details that
will be readily apparent to those skilled in the art, certain
conventional elements and steps have been presented with lesser
detail, while the drawings and the specification describe in
greater detail other elements and steps pertinent to understanding
the embodiments.
[0029] The presented embodiments are not intended to define limits
as to the structures, elements or methods of the inventions, but
only to provide exemplary constructions.
[0030] The following embodiments are permissive rather than
mandatory and illustrative rather than exhaustive.
[0031] For simplicity, the mechanics of an electrospinner system
are described only for the syringe-based, but those skilled in the
art can apply the teachings of the present invention to any
vessel-based system.
[0032] Electrospinning has promise to control fiber formation as it
can produce complex nanostructures with exceedingly precise control
over the shape, size, fusing rate, weave, and fiber thickness. To
accomplish certain of these advantages, a high voltage alternating
signal (i.e., as defined by a signal frequency and peak amplitude)
is used in lieu of a DC voltage. This signal can be applied to the
fluid only, or different signals can be applied to the fluid and
the collector.
[0033] Some interesting effects occur with this arrangement. The
Taylor Cone pulses at twice the frequency of the signal voltage.
This is a result of the continual polarity shift of the signal and
thus the polarity shift of the fluid charge. Herein "pulse" refers
to a peak magnitude (both positive and negative) of the signal
voltage.
[0034] FIG. 3 depicts a 60 Hz sinusoidal voltage with positive
peaks identified with reference numeral 24 and negative peaks with
reference numeral 26.
[0035] At each peak or maximum positive/negative voltage of the
sinusoidal waveform the dissolved material forms into fibers. Those
fibers are charged with the waveform polarity at the time they are
ejected from the nozzle tip and thus the region of the Taylor Cone
carrying those fibers carries the same charge. The fiber charge
polarity alternates at the frequency of the signal voltage. This
changing fiber polarity results in fibers with opposite polarities
that are attracted or repelled from each other to create an
interwoven, interconnected mesh of material as the fibers interact
at the grounded object.
[0036] Various types of materials can be used with the modulated
(or signal based) electrospinner, with the properties of the final
woven product based on the selected material and the charging
signal.
[0037] The frequency of the waveform can be selected to control the
rate of fiber fusing, the tightness of the weave, the thickness of
the fiber, and the shape of the final interwoven mesh. As a general
rule: as frequency increases, the mesh becomes tighter, the fibers
smaller, and more fibers are fused in the formed product.
[0038] Controlling an electrospinner driven by a sinusoidal
waveform is relatively simple when dealing with a single phase,
single frequency signal. The signals can be generated by any number
of devices, but ideally a computer or waveform generator (also
referred to as a signal generator) is used for maximum flexibility
over the waveform shape and magnitude.
[0039] Preferably, the signal is coupled from the signal generator
to an impedance-matched amplifier, then supplied to the
electrospinning fluid. The simplest model of this system is
illustrated in FIG. 4.
[0040] In practice, the system is not as simple as FIG. 4 might
suggest. Most amplifiers increase the power of the output signal
relative to the input signal, but not the output voltage. To
accomplish the latter, a step up high voltage transformer is
required as shown in FIG. 5 with a step-up voltage transformer
disposed between the amplifier and the electrospinning fluid.
[0041] In an embodiment comprising two or more nozzles each
carrying a different material and each driven by a different
signal, an array of high voltage transformers is required, one
transformer for each electrified fluid mass 14 of FIGS. 1, 2B, and
2C.
[0042] While the use of a simple sinusoidal signal to charge the
electrospinner fluid may not be novel, significant material
properties and features can be obtained and the electrospinning
process improved using complex waveforms to charge the fluid.
[0043] For example, according to one embodiment of the invention,
the signal generator supplies a variable frequency signal or a
signal comprising multiple frequencies to the amplifier. The
resulting fibrous structures are more complex than available using
a single frequency signal.
[0044] In another embodiment, multiple frequency signals are used
to charge electrospinning fluids comprised of different materials,
thereby forming hybrid structures on the grounded object.
[0045] For example, to create a large, thick fiber structure with
thin interlacing fibers between each strand, the signal generator
simultaneously supplies both a lower frequency (e.g., 50 Hz) signal
and a higher frequency (e.g., 1 kHz) signal to the fluid. See FIG.
6.
[0046] The use of a multiple-frequency signal creates a complex
structure that is essentially a combination of a structure formed
by a 50 Hz signal and a structure formed by a 1 kHz structure. Both
signals are applied to the same fluid at the same time, resulting
in a complex composite signal.
[0047] An example of such a multiple-frequency signal is
illustrated in FIG. 7, e.g., a combination (sum) frequency signal.
Using such a signal to charge the fluid creates a fibrous material
with unique properties. The higher frequency causes the formation
of a material with a thinner, stronger, and stiffer fibrous
structure, while the lower frequency signal provides a thicker,
more flexible but weaker fiber material. When the combined signal
is applied to a solution comprising only a single material, the
resulting electrospun material is a homogenous mix of the two fiber
types into a single material composite with unique material
properties.
[0048] FIG. 8 illustrates a sum of a 100 Hz and 1 kHz signal. Note
that the 1 kHz signal appears as noise riding on the 100 Hz
signal.
[0049] It should be noted that the number of frequencies that can
be used in the electrospinning process is unlimited and the
selection of specific frequencies is infinite. Only two frequency
signals have been described to simplify the present discussion.
[0050] The characteristics of the resulting fibrous material can be
further controlled by using a multiphase signal, for example, a
three-phase signal. A three-phase signal is illustrated in FIG. 9
with each signal 50, 52 and 54 having the same frequency but the
three signals offset (or out-of-phase) by 120 degrees. This is
found in industrial three-phase power applications such as motors,
but rarely outside of that setting.
[0051] The three-phase signal illustrated in FIG. 9 can be applied
to a single fluid mass (such as the fluid mass 14 of FIG. 1) or in
an embodiment comprising three electrospinning systems (such as
three of the systems 10 illustrated in FIG. 1), one of the three
phased signals applied to each of the electrospinning systems
10.
[0052] The use of multiphase signals in electrospinning provides
additional properties and characteristics by allowing multiple
materials to be simultaneously electrospun. Each material is
electrified individually by one phase of the multiphase signal.
Each phase is used on a different electrospinning fluid to produce
an independent material, or even multiple units of the same fluid.
The phase angle allows for control of interaction between each
independent material. For example, with reference to the three
phase signals 50, 52, and 54 of FIG. 9, each phase charges one of
three different materials that are combined at the ground plate or
drum. Since at any given instant of time the three signals are at
different points along their individual waveforms, a potential
difference exists between the signals and this potential difference
pulls the fibers together into a composite material having a unique
pattern.
[0053] The use of multiphase signals also controls interaction of
each material according to the phase angle between the multiple
phase signals. Again, controlling the phase and/or frequency of the
signals (three in an embodiment with three fiber sources) produces
a material with unique properties.
[0054] The inventors have discovered that as the phase angle
difference between any two of three signals (in a three
signal/three fiber sources embodiment) approaches 180.degree., the
interaction between the two generated fibrous materials
increases.
[0055] The use of multiphase signals allows for the fusing and
interweaving of unlike materials, with the phase angle difference
driving the fusing and interweaving properties.
[0056] For example, if the desired properties of the end product
are conductive, flexible, and relatively strong, a three-signal
system can be used to create a three-material electrospinner system
to produce the end product. Such a three-signal system uses copper
as the conductive material, silicone as the flexible material, and
tool steel as the strong material.
[0057] A 1-to-3 phase splitter can be used to convert a
single-phase signal into a three-phase signal with 120.degree.
between each phase. The fibrous material produced from each one of
the three electrospinners is substantially the same because the
three phase signals each have the same frequency, but they will
come together in the composite material in a unique way. Further
improvements and refinements can be made to this basic three-phase
system as described elsewhere herein.
[0058] To gain better control of the phase angles and in lieu of
using the phase splitter referred to above (resulting in equal
phase angle between every two of the three signals), the phase of
each signal can be independently controlled relative to the phase
of the other signals. This independent control allows exact phase
angles to be specified for each signal relative to the other
signals.
[0059] This is easily done when audio software provides the signal
generating function as each channel can be controlled to operate
independently of the other channels. For higher frequencies,
special high-frequency hardware for signal generation and phase
control can be used. By slightly delaying one or more of the
signals relative to the other signals the phase angle between any
two signals is controlled.
[0060] With reference to the example using copper, silicone, and
tool steel, the phase angle between the copper and steel is
controlled to a fairly shallow value (about 20.degree. or so) and
the phase angle of the silicone to be 170.degree. out of phase with
each metal. This is feasible approach because phase angles have a
ceiling of 180.degree. and a floor of -180.degree., resulting in a
functional 360.degree. of phase difference available for
manipulation.
[0061] The signals driving the copper and steel electrospinning
processes are set with a relatively small phase angle difference
because each of those materials is a crystallized metal. The phase
angle for the silicone process is significantly offset from copper
and steel because the silicon is an amorphous solid, unlike copper
and steel. With such independent phase angle control the structures
as formed by each material will be substantially the same as if
they were electrospun independently, except for the fact they will
bind and weave with the other materials electrospun
simultaneously.
[0062] In another embodiment, in addition to independent control of
the phase angles of the three (or more or fewer) signals, to
provide more control over and more variability in the electrospun
material, each signal frequency is independently controlled to a
different value.
[0063] The concept of a phase angle difference between two signals
is particularly problematic because by definition, a phase angle
difference can exist only between two signals of the same
frequency. For example, the phase difference between two 60 Hz
power line signals. Thus, the scope of the present invention
includes as least two or more same-frequency signals at different
phase angles and two more signals of differing frequencies.
[0064] Additionally, if the signals are improperly manipulated (as
caused by poor reproduction of the signal in a carrier wave of low
fidelity) signal integrity cannot be maintained. Noise and
harmonics can cause signal distortions that cause unwanted physical
properties in the electrospun material.
[0065] This difficulty is resolvable by using square waves where
possible to modify the signal as set forth in the equation
below.
phase leg = A 1 .times. ( 2 .pi. f + .PHI. ) + A 2 s 1 + s 2 + s 3
+ + s n n Phase setting equation for unlike signals Equation 1
##EQU00001##
Where A.sub.1 is the amplitude of the square wave envelope or
carrier signal, A.sub.2 is the amplitude of the individual
electrospinning signals, .pi. is the square wave function, which
can in other embodiments be any waveform. A square wave tends to be
an ideal choice (but not a necessary choice) because it does not
distort the signal output to the electrospinner, f is at least half
of the lowest frequency component from the signal (if the lowest
frequency within the electrospinning frequency is 60 Hz, then f
should be 30 Hz or less). In another embodiment, this can be larger
than half, but it will begin to "chop" the signal. .phi. is the
desired phase angle of the signal driving one of the fiber sources
to the specific material, which can be at the user's discretion for
a given application. s.sub.x represents the individual frequency
components that make up the signal and can represent any periodic
signal such as sine, cosine, square, saw-tooth, or another
repeating signal. It can be any time variant signal such as a radar
sweep or any variation in signal magnitude, which may not define a
known waveform function. Finally, n is the number of frequency
components within the signal, to normalize the magnitudes of each
component within the overall signal.
[0066] Most of this equation is easily derived from empirical data
and simulation, but the f is intuitive and based upon Nyquist's
Theorem. If a signal is manipulated to fit within a slower carrier
wave, usually square wave, as a means of creating a phase the
signal should be able to complete at least one cycle before being
inverted by the carrier wave. This carrier wave is used in each
phase leg (each independent power line) at the exact same frequency
but the phase angle between each leg is controlled from by the
user. If, for example, the composite signals generated as described
elsewhere herein are attempted to be set with a phase angle
relative to each other.
[0067] FIG. 10 illustrates a square envelope using unmatched
signals without setting a specific phase angle between the signals.
Very little interaction occurs between the two signals of the
electrospinner because there is no existing phase angle, nor is
there much voltage potential difference between the signals.
[0068] Instead, if a square wave of 50 Hz and a phase angle of
.pi. 2 ##EQU00002##
(or 90.degree.) are used in Equation 1, the resulting signal is
shown in FIG. 11. See also FIG. 12, which illustrates a composite
signal.
[0069] The signals clearly have a phase relationship to one
another, and now can be used as if the system signals were the same
in each line. This allows for a multifrequency, multiphase system
to operate with independent and distinct phase legs, resulting in
unique structures for each material while still having the phase
based interelated.
[0070] The extent of the interaction can be estimated based on the
area between the two curves, which is an integral of the voltage
over change in time.
[0071] Note, there are downsides to working with multiphase
signals. The peak-to-peak voltage (Vpp) in the original signal is
now
1 n ##EQU00003##
of what it was before the manipulation, but the overall Vpp is
still the same. Simply put, to pack more sub signals into the
electrospinning signal, each one has a smaller impact as their
amplitudes diminish. The amplitude of the overall signal is not
changed, but the impact of each sub component or sub signal as more
are added is reduced. This is reversable by merely running the
system at an amplitude of nA.sub.2 to compensate, but the overall
system must be capable of the new amplitude.
[0072] In an electrospinning system that uses multiple signals at
different or the same frequencies and different phase angles for
the same-frequency signals, with multiple materials, with the
signal frequency, phase, and amplitide independently controlled,
provides the ability to form a composite material having desirable
properties. Such a system is a substantial improvement over a
single frequency system as in the prior art.
[0073] To create a multifrequency signal, the signal generator must
be able to produce more than one frequency, and combine them as
needed for the application. Computer software is still the ideal
signal generation, either audio software for lower frequencies such
as Audacity, or for higher frequencies on a custom signal output
hardware, MATLAB or a similar software-controlled signal generator
is acceptable.
[0074] The use of multiphase signals demands a multichannel output
that has precision timing controls, such as that of a
surround-sound system for lower frequency uses, or a custom
hardware system built to desired specifications.
[0075] A block diagram of such a system is set forth in FIG. 13,
which depicts a three-phase system for controlling three
electrospinners, but any number of phased signals and
electrospinning systems can be used.
[0076] The three phases and the components associated with each
phase bear the same numerical reference (1, 2, and 3). As in the
embodiment of FIG. 5, the signal generator outputs to the
amplifier, which in turn feeds the signal to a transformer the
outout of which controls ejection of the electrospinning fluid. A
transformer array merely comprises a bank of transformers with each
transformer responsive to a different signal so that the array
handles multiple phases. Each phase requires at least one
transformer, and if more than one is required, the transformers are
connected in series. The principal difference with the FIG. 5
single signal embodiment is that the signal generator and amplifier
of FIG. 13 must be multichannel for the multiphase system to
operate properly.
[0077] In another embodiment, due to the limitations of modern
amplifiers at higher frequencies, older technologies have been
used, as they offer distinct advantages over modern approaches. In
one embodiment, the older technology involves the use of vacuum
tubes, more specifically, power beam tetrodes.
[0078] The design presented herein is only an exemplary model; as
those skilled in the art are aware other designs can be utilized.
However, this technology offers certain advantages within the scope
of the present invention, which may be referred to as a multi-phase
variable frequency signal modulated electrospinner. It is therefore
a viable and appealing alternative to the use of transformers or
semiconductors.
[0079] Transformers are by far the most common device for
increasing (or decreasing) a voltage. Through a simple induction
process using proximate wire coils, a transformer can increase or
decrease an input voltage with reasonable (if not exemplary) power
efficiency. The ratio of turns between a primary and a second coil
dictates the ratio of voltage increase (and current reduction).
[0080] For example, a 120 Vrms input to a primary coil having 120
turns paired with 2,000 turn secondary or output coil results in a
2,000 Vrms output. Use of a ferromagnetic core located to increase
the coupling between the primary and secondary coils improves the
efficiency and reduces transformer losses. By this example, it
seems there is very little limitation to what a transformer can
do.
[0081] The primary transformer limitation relates to the core
material. Standard transformers have a laminated iron core, which
consists of thin sheets of epoxy-coated metal oriented orthogonally
to the coil windings. This arrangement provides efficient magnetic
field permeation through each sheet of metal without significant
losses due to electromagnetic eddy currents.
[0082] These losses manifest in the form of heat, which if left
unchecked will melt the core. This "inefficiency" is the premise of
an induction forge, which are purposefully designed to use this
phenomenon to superheat metals.
[0083] The problem of eddy current losses becomes more pronounced
as the frequency increases. With higher signal frequencies, more
"electrical friction" is generated via eddy currents and core
overheating becomes more likely. By using more exotic metals, such
as amorphous or silicon steel, when working in audio frequencies or
higher (400 Hz to 100 KHz) the risk of overheating the transformer
core is reduced, but efficiency drops significantly after the
applied signal frequencies reach about 80 kHz.
[0084] Ferrite cores and air cores (meaning a lack of a specific
core material) are the standard for higher frequency applications,
though some of the system's efficiency and flux density are
sacrificed. The flux density dictates how many turns per volt are
required before core saturation occurs. The less ferromagnetic
material contained within the core, the lower the flux density and
thus more turns of wire are needed per coil for the same voltage.
This means that if an air core is needed because of a high
frequency application, the number of turns for the same voltage,
input and output, will be much higher than a lower-frequency system
implemented with an iron core. For example, in a step-up
transformer increasing 120 v to 240 v, with a good silicon steel
core, the flux density is 1 v per turn, so the primary is 120 turns
and the secondary is 240. In an air core transformer with similar
cross sectional area it may be much lower such as 1 v per 8 turns,
and thus the primary has 960 turns and the secondary has a 1920
turns. Note the ratio between the turns stays the same, but the
amount of wire needed increases dramatically.
[0085] These extra turns also lead to parasitic capacitances
between the windings of the coil and the increased resistance of
the longer wire required to form the appropriate number of coil
turns. These inefficiencies exist in every transformer, but they
are negligible if the frequency and number of turns are both
relatively low. As frequency increases, the stray inductance of the
non-ideal coils and the parasitic capacitances result in an even
larger energy loss and can eventually lead to distortions in the
signal. These distortions may be considered as an "interfering
signal" and change the properties of the electrospun material. This
is because each distortion is frequency dependent and different for
each unique system. Even with the best shielding, these coils will
pick up other signals and interferences that will provide a
challenge to maintaining the necessary level of signal
fidelity.
[0086] As the signal frequency increases, the impact of these
capacitances increases. There exist resonant frequencies where the
signal can no longer flow based on the reactance (induction based
resistance) and impedance (capacitor based resistance) reaching
critical levels of resisting flow. Excluding those effects, of
course there is still a distortion of the signal that changes based
on the frequency; this distortion is difficult to counteract.
[0087] Another technique to achieve signal amplification involves
the use of semiconductor transistors, such as high-speed MOSFETs.
Frequency is not much of a problem with MOSFETS as long as their
gate speed is capable of functioning at the frequency of the input
signal. Their principle limitations are related to lack of high
voltage capacity, low durability to heat, and overvoltage risks.
Another limitation of transistor technology is the low voltage
ceiling. Any high-voltage applications would require the use of
transformers as a secondary component on the output side.
[0088] Semiconductor transistors also can suffer from a limited
resolution since they are normally used with digital components.
The digital use of the transistor is double edged; it can be used
readily with digital controllers and it provides functional
flexibility, but this means it has a set resolution and signal
integrity. With applications for highly-sensitive manipulation of
matter using modulated signals, signal fidelity is extremely
important. Any distortion is seen by the material as a new
"frequency," which can impact the material properties.
Implementation of digital amplification components would require
that the input signal at some point be converted into a digital
format of some set resolution, which inherently negatively impacts
the signal's quality. However, if the signal source is digital and
all resolution/bitrate data is matched in the rest of the system,
it can be accounted for. This results in a known distortion that is
applied in a repeatable manner to the electrospinning fluid, so
being known and intended the resulting properties of the material
are a result of the source signal (the intended frequencies it is
constructed of) and the digital resolution of the signal (the
unintended frequencies of finite digital resolution).
[0089] Vacuum tube amplifiers can also be used with the present
invention, but they too have limitations. They run very hot, are
physically fragile, are (relatively) large, and can generate
distortion that is difficult to remove if improperly designed.
[0090] Triodes are notorious for having parasitic capacitances
between the grid and anode, resulting in massive energy
inefficiencies and even signal distortion at higher frequencies.
This can be addressed by adding a screen between the grid and
anode, thus creating a tetrode tube system. The aforementioned
screen provides a means of limiting the backflow of electrons as
well, improving the overall efficiency of the system. The
efficiency is worse than a triode at lower frequencies or a pentode
(generally) unless the cathode is used to direct the flow as in a
power beam tetrode. The cathode is brought up to encompass the grid
and screen to force the electron flow as "plates" perpendicular to
the anode (aka "beams"), which drastically improve efficiency. That
being said, any vacuum tube provides the following benefits at
varying levels of efficiency.
[0091] FIG. 14 depicts four types of vacuum tubes: a triode 44, a
tetrode 45, a power beam tetrode 46, and a pentode 47. Each name is
based on the number of components in the tube. Reference character
49 denotes a heater, 50 denotes a cathode, 52 denotes an anode or
plate (output), and 53 denotes a grid (signal source), 54 denotes a
screen (reduces capacitance between the tube components), and 55
denotes a secondary screen (to further reduce capacitance).
[0092] In the power beam tetrode 46, the cathode 50 substantially
surrounds the grid 53 and screen 54 to focus the electron flow to
the anode 52.
[0093] With a well-designed vacuum tube system, these limitations
are heavily minimized and the value of using them in this
application become clear. They lack the frequency ceilings that
plague transformers, they do not have the resolution distorting
potential of semiconductors, they can operate at very high
voltages, they are rugged electrically and thermally, and they do
not fail if too much voltage is applied.
[0094] For an application such as multi-phase variable frequency
signal modulated electrospinner, this is ideal since such a system
requires the ability to amplify a high-frequency signal to very
high voltages with as little distortion as possible. In the correct
circuit, vacuum tubes are the ideal amplifying mechanism for
electrospinning applications.
[0095] FIG. 15 is a schematic example of a vacuum-based system.
With a single tube, the system is relatively simple with some
valuable features: the signal is isolated, the tube and power
supply are grounded to ensure that the system does not have issues
with floating voltages, variable resistors are used to allow for
calibration of the heating element and the DC bias applied to the
signal.
[0096] Signal isolation is ideal, but not necessary, for such a
device to reduce signal feedback and limit the risk of damaging the
signal source. Grounding is a given when dealing with high voltage
to reduce the chance of dangerous voltage floating. This also
ensures that the collector plate has the same voltage potential as
the reference leg of the amplified signal. One limitation presented
by this system is that the maximum voltage of the system is based
on a single tube, which could be doubled (if necessary) by using
the dual-tube system of FIG. 16.
[0097] This system is a single "unit" in a larger design made up of
repeating segments. By using multiple units in one system, it is
possible to create a complex multiphase system. The two-tube unit
has three distinct advantages over a single tube unit: the tubes
can be used individually or in tandem, half of the number of power
supplies are required, and less space is needed for the same number
of tubes. To use them in tandem, the reference leg of the DC
components are set to floating ground, and the output of one of the
tubes is set to ground. Floating ground refers to the internal
reference that is counted as the negative line, or neutral line, or
negative and neutral line depending on if the current is DC or
signal based. The signal (which is same to both tubes) sent to each
tube is 180.degree. out of phase to create double the voltage
amplification of a single tube. By sharing the power supply, the
two tubes can work together or separately by flipping two
switches.
[0098] In the multiphase system configuration, each unit, or each
amplifier pair (in this case vacuum tubes) can be used as a phase
or each amplifier can be used independently, as well. For example,
in a five-unit system with each unit comprising a two-tube system.
If the tubes are rated at 5 KV each, there are eight total phases
needed and two of them need to be 10 KV--this is quite feasible for
this system. Two units will be configured for tandem function of
the tubes, while three units will have each tube operate
independently. This is just one example of an indefinite number of
possible system configurations, especially if the docking system
for the units in question is made modular or expandable.
[0099] FIG. 17 illustrates a three unit system with either six 5 KV
outputs, or three 10 KV outputs, and/or any combination of the
two.
[0100] Another embodiment employs both analog and digital
components for providing computer-based control. Such a system can
be implemented in at least two exemplary embodiments, but anyone
skilled of signal generation knows there is no limit to how the
signal is produced and controlled digitally.
[0101] At lower audio frequencies, one can use Audacity, a free
audio editor, and a sound card to operate it at upwards of eight
phases (7.1 surround sound, using each available channel as an
input having a unique phase angle).
[0102] At higher frequencies, a more advanced system can be
implemented using MATLAB or LabVIEW and an external digital signal
generator would be necessary.
[0103] Manual generation of input signals via analog means and
combining frequencies with complicated junctions is not easily
viable, especially when scaling to a commercial/industrial level.
To achieve the best results from a multi-phase variable frequency
signal modulated electrospinner, digital signal generation combined
with a well-calibrated analog amplifier provides precise signal
control, generation, and amplification with minimal signal
distortion and degradation. Digital resolution of the signal
generated is easily accounted for when the characterization of a
material is done. An example of this occurring would be a digitally
produced 500 Hz, 5 v signal with a 44 KHz bitrate and a resolution
of 5 mV. It would act as a signal with two unbalanced components, a
large 500 Hz frequency and a small but present 44 KHz frequency.
Changing signal resolution and bitrate can result in different
properties in the material end product by inducing different
"frequencies" in the signal based on the resolution and bitrate
size.
[0104] FIG. 18 depicts limitations on the use of digital
amplification on a high fidelity application, such as
electrospinning. If multiple digital systems are used in tandem
without matching resolution, there is a loss of signal integrity by
introducing a resolution to the signal. The "steps" generated in
the signal from the resolution can degrade the quality of the
signal, and if multiple digital systems are used, then the signal
has multiple types of mismatched steps embedded within.
[0105] A tube-based system, does not subject the signal to another
layer of resolution modification, and thus does not result in
signal degradation. Analog degradation can be compensated for
either with impedance matching or similar mechanisms. These issues
occur with or without digital systems, and would have to be
compensated for in either scenario. As mentioned elsewhere, the
signal's digital fidelity in the form of its bitrate and resolution
is not a concern when the signal is generated as long as it is
accounted for by estimating the "frequency" and "amplitude"
modulation imposed by the digital bitrate and resolution. The
resolution height (or step height) is the amplitude of this
sub-frequency, while the bitrate (or value change per second)
determines its frequency. For most applications, the signal
stepping is negligible, but in electrospinning it will not be.
Structures in the resulting material output will be impacted based
on the digital resolution and bitrate. This would manifest as the
main signal as the carrier signal, and the digital stepping would
appear as a riding signal on the carrier.
Metal Mesh Production Using Multi-Phase Variable Frequency Signal
Modulated Electrospinner of the Present Invention
[0106] Building on the previous discussions and in tandem with the
Carbon Mesh section below this sections describes an application of
the multi-phase variable frequency signal modulated
electrospinner.
[0107] Metal meshes have a wide range of applications based on
fiber size, metal type, and structure. For example, iron is the
standard base metal for most mechanical equipment because of its
diverse properties that depend on the impurities that are added
such as carbon or chromium. If manipulated into a mesh, iron can
become a lightweight "foam" that allows for high strength
applications with weight restrictions. As mentioned before, this
can be combined with the multiphase components to have hybrid
metals and composites.
Using Iron
[0108] Iron has significant properties and applications and
deserves to be discussed separately. Being such a versatile metal,
controlling it on a nanoscale in the multi-phase variable frequency
signal modulated electrospinner would be ideal for precision
engineering applications. To achieve this, the iron has to be in a
form that can be dissolved into a solvent without risk to the user
or machinery. The implementation of metal salts is an ideal
technique for achieving this, and an exemplary form of this is iron
nitrate. It is water soluble, readily made, and is fairly inert. It
has to also have a charge retaining component (aka an insulating
material) which with a standard plastic solute electrospinning
fluid, is the plastic itself. To rectify this, a plastic additive
is combined with the metal salt to provide charge maintenance.
Polyvinyl Alcohol is an exemplary material to add because of its
water solubility and the high charge potential it has as a
plastic.
[0109] The electrospinner system is set up as described above, but
uses the aqueous Polyvinyl Alcohol Iron Nitrate solution as the
electrospinning fluid. Once electrospun, the fibers can receive
specific treatment to stabilize them and remove the plastic
components. If heated above the vaporization temperature in an
atmospheric environment, the plastic evaporates, the iron oxidizes,
and the ensuing oxide stabilizes. If done in an inert gas
environment at similar temperatures, the plastic carburizes on the
iron and no oxides form. The plastic can be left of course, if the
application needs an iron based mesh bound to a plastic.
[0110] FIG. 19 is a scanning electron micrograph that depicts an
iron nanomesh as produced using the present invention by one of the
inventors. The scale bar at the bottom of the photo is 5 um and the
illustrated sample has been heat treated to remove the residual
plastic in an atmospheric environment.
[0111] FIG. 20 is a zoomed out image of the metal fiber mesh has a
scale bar of 10 um displaying the homogenous and isotropic nature
of the metal nanomesh production with the multi-phase variable
frequency signal modulated electrospinner.
Other Metals
[0112] To use other metals, the only change needed is to exchange
the iron nitrate for a different metal salt, such as copper sulfate
or silver nitrate. Metal salts that are soluble in water are ideal,
and an exemplary list is given below: [0113] Ferric nitrate [0114]
Cupric sulfate [0115] Aluminum sulfate [0116] Barium chloride
[0117] Beryllium sulfate [0118] Cadmium sulfate [0119] Calcium
chloride [0120] Chromium nitrate [0121] Cobalt nitrate [0122]
Lanthanum chloride [0123] Lead acetate [0124] Magnesium chloride
[0125] Manganese sulfate (or pure manganese if the solvent is
water) [0126] Mercuric nitrate [0127] Nickel nitrate [0128]
Potassium tellurite [0129] Rhodium trichloride [0130] Potassium
tetraoxalate [0131] Sodium carbonate [0132] Stannous chloride
[0133] Strontium chloride [0134] Titanium tetrachloride [0135] Zinc
nitrate
[0136] Water and polyvinyl alcohol will work for most applications,
but can be changed or adjusted to other solvents and plastics
depending on the capacitance and conductivity needs of the
electrospinning fluid. The basic process of producing the iron
nitrate fluid is well documented and well known, but an exemplary
method will be provided below as a generic chemical process for use
with other metal salts.
[0137] Polyvinyl Alcohol Solution: [0138] 1. Add 1 part by weight
of Polyvinyl Alcohol to standard glassware [0139] 2. Fill with 9
parts by weight DI water [0140] 3. Add magnetic stir rod, placing
the solution on a heated stir plate running at 50-90.degree. C. and
a high rpm (700-1500) respectively [0141] 4. Run for 3-4 hours
until clear and homogenous
[0142] FeNO.sub.3 Aqueous Solution: [0143] 1. Place 3 parts by
weight of FeNO.sub.3 into glassware, adding 4 parts by weight of DI
water to it [0144] 2. Stir manually until homogenous
[0145] Polyvinyl Alcohol FeNO.sub.3 Final Solution: [0146] 1. Add
the Polyvinyl Alcohol solution to the FeNO.sub.3 solution in a
range of 4:1 to 9:1 parts by weight [0147] 2. Place on heated stir
plate for 5 hours at a high rpm, or until homogenous This method
should also work with the other metal salts with little to no
modification. Combining with Multiphasing
[0148] As with other materials, this use of various metals can
benefit from the multiphase component in the multi-phase variable
frequency signal modulated electrospinner to create hybrid
materials. For metal to metal, the phase angle can be relatively
small because of metallic bonds between each type of metal, which
help to form a stable inter-material weave. As other materials are
used in the multiphase electrospinning system, the phase angle will
need to be increased to handle the dissimilar materials and force a
bond between them.
Applications in Industry
[0149] For iron, there are several applications that bear
themselves in a variety of industries. In the case of oxidized iron
(formed when electrospun material is stabilized in an atmospheric
environment), the resulting iron can be any type of oxide from
magnetite to hematite or a combination of both depending on a
specific need. Magnetite, hematite, and their combinations are
exemplary for making heavy metal absorbing components for water
filters. If the iron is not oxidized, such as when the samples are
heat treated in an inert environment, the iron can be used as a
catalyst for producing dozens of chemicals. This interwoven fused
mesh formed in a micro- or nano-scale would be ideal for such
needs. An example where the mechanical structure would matter is
when such an iron catalyst would be used to produce carbon
nanotubes (CNT). By controlling the shape of the catalyst, one can
control the shape of the CNT and even the functionality of the
tubes.
[0150] The signal modulated electrospinning process is not limited
to pure iron of course. By adding other "impurities" to the
electrospinning solution, one can form structures such as
cementite, or even different steel types. This can be extended to
other metals and their alloys, and each can be produced and
dissolved into an electrospinning solution to create multi-phase
variable frequency signal modulated electrospinner-compatible
materials.
[0151] One of the more interesting applications of having a high
surface-area-to-volume ratio in a metal is that the resulting
material would out-perform today's existing materials. With
aluminum for example, anodization creates a strong, durable, super
hard, high temperature, and chemically resistant coating over the
surface of the aluminum by converting the surface layer into
aluminum oxide. This layer thickness is normally 2 .mu.m, but if
the fiber size in the electrospun mesh is smaller than that, then
the entirety of the bulk aluminum can be converted, as well.
[0152] Similarly, with steel alloys, nitride processing produces a
chemical hardening of the metal surface without compromising
ductility or strength at higher temperatures like traditional
hardening. The layer depth of nitride work is about 5 .mu.m deep,
which is much larger than the radius of the fibers in the iron
nanomesh. If gas nitride (or even with cyanide salts or Quench
Polish Quench), the entire bulk material becomes fully hardened
steel (60RC) that can handle temperatures in the red hot
temperature range before the temper/hardness is lost, compared to
standard hardened steel where anything over 110.degree. C. can
damage the temper of a piece of equipment. These materials can be
used for petrol engines, high-temperature turbines, and any
industrial machinery that has to withstand higher temperatures and
with a hardness as large as possible.
Methods for the Production of a Novel Carbon Mesh Composite
Material
[0153] The composites industry in the United States alone is
estimated to be approximately $8.2 billion, and is projected to
reach $12 billion by 2020. Carbon fiber composites dominate the
industry across a majority of composite applications, and its use
is limited only by the rate and efficiency at which it can be
produced.
[0154] Carbon fiber is used extensively in a variety of
applications including wind turbines, protective equipment in
recreation and industrial applications, and as lightweight and
high-strength materials in high-end automotive, boating, and
aerospace platforms.
[0155] Current manufacturing methods offer only a low profit margin
and a limited ability to produce carbon fiber at a rate which would
be sustainable in high-demand applications such as the general
automotive industry. With the implementation of methods disclosed
here, it is possible to eliminate several stages of the existing
manufacturing process--saving time and resources, while
significantly cutting production costs.
Benefits of Using Multi-Phase Variable Frequency Signal Modulated
Electrospinner with Carbon Fiber
[0156] The disclosures herein refer to the various stages of a
novel process for the production of a new carbon mesh composite
material similar to existing carbon fiber composites. The material
produced as a result of these processes has properties comparable
to traditional carbon fiber, and holds some advantages over the
traditional material as well.
[0157] The carbon mesh comprises fibers with diameters that can
controllably range from the micron scale to the nanometer scale.
These fibers are connected to one another at different points
(hereon referred to as "nodes") and are arranged pseudo-randomly in
terms of fiber alignment. This pseudorandom alignment provides
isotropic mechanical properties, an important advantage over
mechanically woven carbon fiber cloth, or tow. Where panels of
traditional carbon fiber would typically require several layers
oriented along different axes to achieve an artificial isotropic
state in terms of strength, the proposed carbon mesh would be
inherently isotropic and would require additional layers only to
achieve the desired strength with no consideration for orientation
necessary. The existence of the aforementioned nodes also provides
an additional source of mechanical strength, allowing loads to be
distributed across more of the carbon mesh at any given point.
Since carbon fiber cannot be directly electrospun into a continuous
material, electrospinning a precursor material is necessary
followed by post processing.
Manufacturing and Production
[0158] The creation of the disclosed carbon mesh requires
specialized equipment and processes. The first stage of the process
involves the production of the carbon mesh precursor material. In
order to produce the precursor required for carbon mesh, an
appropriately-designed electrospinning system must be used. This
electrospinning system may consist of one or more vat reservoirs,
continuous material feeding system, a user-controllable interface,
one or more syringe dispensing arrays, driving electronics, a
collecting element, electromagnetic field (EMF) shielding,
mechanical means of maintaining uniform solution concentrations of
the electrospinning materials, conductive elements to convey
electrical charge to the electrospinning solution, or any
combination thereof that is deemed necessary to accomplish the
desired result depending on the application in consideration.
[0159] In an appropriately designed electrospinning system
implementation, the user should be able to create conditions in the
manufacturing process wherein the precursor mesh will consist of
fibers of a specific diameter range, deposition rate, and node
formation rate, among other things. This configurability provides
the ability to determine the mechanical properties of the final
carbon mesh product through computer-based control. This
electrospinning system may exist as part of a larger assembly line
or conveyor system that directly and continuously feeds precursor
material into the succeeding stages of manufacturing, or it may
deposit material onto a static collection mechanism that allows for
production of precursor material to be used in a separate
post-processing system. Such a conveyor system would consist of a
series of pulleys or rollers, any number of which having the
capability to be used as a tensioner pulley or roller not unlike
those used in automobile belt trains. A conveyor-belt-like
apparatus would rotate about the collector mechanism, carrying away
the electrospun precursor mesh at the configured line speed. The
conveyor belt should consist of a chemically-resistant material
such as Mylar. At some point in the conveyor system, the material
will detach from the conveyor belt and travel on to subsequent
stages of the process continuously via the aforementioned
pulleys/rollers.
[0160] At least one motor should be incorporated directly or
indirectly to drive rotating motion in one or more of the
rollers/pulleys, and should allow for digital and/or analog control
of conveyor system speed with or without the implementation of
feedback loops utilizing sensor and MCU technology.
[0161] Due to the unique structure of the proposed carbon mesh,
many unique manufacturing considerations need be addressed. The
process may be implemented with any carbon fiber precursor
material, though polyacrylonitrile will be used as an exemplary
case in this disclosure. With Polyacrylonitrile based carbon fiber
production, it is important to keep the precursor material under
tension through different stages of processing. In traditional
carbon fiber manufacturing, individual fibers are extruded via one
of many different commonly used methods, pre-processed with acid
etching, then conveyed through several stages of fiber shaping,
sizing, and heat treatment.
[0162] Maintaining fiber tension in this process is relatively
straightforward in this case since the only force which is required
is along the direction of the manufacturing line. In this the novel
system herein described, carbon mesh precursors have randomly
arranged fiber orientations, and it is important to apply tensile
forces in as many directions as possible on the material. One
proposed method involves the application of specially-shaped
pulleys or rollers which stretch the carbon mesh sheet in many
different directions as it passes through different stages of the
manufacturing process.
Chemical Considerations and Heating
[0163] When solvent electrospinning is implemented, or any form of
dissolving the material to electrospin into a solvent, it is
important to ensure that the solvent is fully removed before the
heat treatment stages begin. To achieve this, the precursor is
exposed to some spray or bath consisting of a chemical specifically
chosen to neutralize the potentially hazardous solvent. In the
exemplary embodiment utilizing Polyacrylonitrile-based precursor
mesh dissolved in dimethylformamide (DMF), a simple water-spraying
mechanism can be implemented in series with heating elements to
remove the given solvent in the precursor before it enters the
first stage of heat treatment. Like standard
Polyacrylonitrile-based carbon fiber manufacturing, the precursor
mesh will pass through a minimum of two stages of heat
treatment.
[0164] The first stage will be herein referred to as the
"stabilization phase", and the second will be referred to as the
"carbonization stage". In the preferred embodiment, each of these
stages will take place in separate furnace systems capable of
reaching the appropriate temperatures. In different embodiments the
temperature required for stabilization may range from 100.degree.
C. to 1000.degree. C., while the temperature required for
carbonization may range from 1000.degree. C. to 3000.degree. C. The
time that the material remains at each stage of heat treatment will
vary and can be adjusted to correlate appropriately with parameters
of the manufacturing system as well as the desired properties of
the final carbon mesh material. During stabilization, the material
should be exposed to an oxygen-containing environment, such as the
atmospheric condition, to allow for the appropriate chemical
reactions to take place. During the carbonization phase of the heat
treatment, the mesh should only be exposed to an inert gas
environment to prevent oxidation and/or ignition of the material.
The heat treated mesh may then be sized with typically one or
several polymeric components, a coupling agent, a lubricant and a
range of additives to protect it while it is collected on a spool
or as it goes through further processing, including molding.
Coating the fibers to optimize them for future use is standard
practice and can be easily applied to the produced carbon fiber
mesh produced with the aforementioned signal modulated
electrospinner.
[0165] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to make and use the invention. The scope of the
invention may include other examples that occur to those skilled in
the art. Such other examples are intended to be within the scope of
the claims if they have structural elements that do not differ from
the literal language of the claims, or if they include equivalent
structural elements with insubstantial differences from the literal
languages of the claims.
* * * * *